1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms images by using toner.
2. Description of the Related Art
An image forming apparatus typically includes a photosensitive drum, and a charging device, an exposure device, a developing device, and the like that are arranged around the photosensitive drum. The surface of the photosensitive drum is uniformly charged by the charging device, and the charged part is exposed to layer light emitted by the exposure device. As a result, an electrostatic latent image is formed on the photosensitive drum, and the electrostatic latent image is developed by the developing device into a toner image.
The toner image on the photosensitive drum is transferred onto a sheet conveyed by a conveyance belt. The sheet onto which the toner image is transferred is separated from the conveyance belt and conveyed to a fixing device, where the toner is fixed and the sheet is discharged.
The fixing device includes a fixing belt for heating and applying pressure to the sheet.
For example, if fixing onto an A4 size sheet fed in the portrait direction is repeated in an image forming apparatus capable of using A4 size sheets and A3 size sheets, a vertical crack may be caused at a position where ends of the A4 size sheets in the sheet width direction on the surface of the fixing belt. This is because the surface of the fixing belt is roughened by paper powder from the sheet ends.
In this case, when an A4 sheet is fed in the landscape direction or an A3 sheet is fed in the portrait direction, what is called a glossy stripe is caused on the surface of the image corresponding to the vertical crack, which degrades image quality.
Image forming apparatuses considering roughening of the surface of a fixing belt have therefore been devised (for example, refer to JP 5-113739 A, JP 4632820 B1, JP 2007-34068 A, and JP 2010-262023 A).
The demands for higher image quality of image forming apparatuses are increasing every year. With the image forming apparatuses disclosed in JP 5-113739 A, JP 4632820 B1, JP 2007-34068 A, and JP 2010-262023 A, however, it is difficult to achieve the required level of image quality.